The present invention relates generally to the field of limiting temperature in electronic apparatus and more specifically to the use of a temperature-sensitive impedance to alter a potentiometer set point signal.
In a wide variety of applications, a potentiometer is used to provide a set point signal to an electronic apparatus. The set point signal is first among a series of signals and functional elements constituting a primary control path through the electronic apparatus. In response to the primary control path signals, the electronic apparatus performs a primary function. Performance of the primary function typically generates heat, either as an intended product, as in, for example, a cooking appliance or other heating application, or as an unintended by-product owing to electrical power dissipation in component resistances. To curtail an excessive, potentially damaging temperature rise, either inside or outside the electronic apparatus itself, at least a portion of the electronic apparatus is conventionally devoted to a temperature limiting function often realized by closing a temperature feedback loop through a secondary control path. When the secondary control path includes an unstable compensator, such as, for example, an integrator, an additional anti-windup function is typically performed through a tertiary control path.
The three-path temperature limiting scheme has numerous benefits: flexibility in choice of temperature limit; the possibility of having temperature limit dynamics different from primary function dynamics; the ability to use unstable temperature compensators providing higher performance, in some cases, than alternative stable compensators; and an explicit classical control structure facilitating analysis and prediction of dynamic behavior.
However, in some applications, such as, for example, in some cooking appliances, it is economically advantageous to sacrifice some of the abovementioned benefits in order to reduce the overall cost and complexity of the electronic apparatus. An opportunity exists, therefore, to eliminate the secondary and tertiary control paths by modifying the primary control path to perform both the primary function and the temperature limiting function.
The opportunity described above is addressed, in one embodiment of the present invention, by replacing a user interface and a temperature sensing interface with a single temperature limiting user interface comprising: a potentiometer for providing a reference signal to an electronic apparatus, the electronic apparatus being adapted to generate heat as a function of the reference signal; and a temperature-sensitive impedance, thermally coupled to the electronic apparatus so as to receive at least a portion of the heat, and electrically coupled to the potentiometer so as to alter the reference signal as a function of temperature.